Abstract
Sunlight absorbed at the Earth’s surface is re-emitted as longwave radiation. Increasing atmospheric concentrations of CO2 and other greenhouse gases trap an increasing fraction of such heat, leading to global climate change. Here we show that when a chlorophyll (Chl)-deficient soybean mutant is grown in the field, the fraction of solar-irradiance which is reflected, rather than absorbed, is consistently higher than in commercial varieties. But, while the effect on radiative forcing during the crop cycle at the scale of the individual experimental plot was found to be large (−4.1± 0.6 W m−2), global substitution of the current varieties with this genotype would cause a small increase in global surface albedo, resulting in a global shortwave radiative forcing of −0.003 W m−2, corresponding to 4.4 Gt CO2eq.At present, this offsetting effect would come at the expense of reductions to yields, probably associated with different dynamic of photosynthetic response in the Chl-deficient mutant. The idea of reducing surface-driven radiative forcing by means of Chl-deficient crops therefore requires that novel high-yielding and high-albedo crops are made available soon.
Highlights
Croplands currently occupy 11.97% of the global land surface (FAO 2020)
Increases in albedo may contribute to reducing the current increase in longwave radiative forcing (RFLW ) which is caused by the rise of atmospheric well-mixed greenhouse gases (GHGs; by 3.1 W m−2 in 2015 since the pre-industrial era) (Lenton and Vaughan 2009, Myhre et al 2017, Mayer et al 2018)
Shortwave reflectance measurements based on both field and satellite data in 2016, 2017 and 2018 showed that the albedo of MinnGold was consistently higher than the albedo of the green varieties
Summary
Croplands currently occupy 11.97% of the global land surface (FAO 2020). Agriculture must maintain or increase crop yields (greater production over a smaller land surface), while maximizing its environmental benefits. Modelling experiments have repeatedly shown that higher cropland albedo may effectively mitigate the magnitude of future heatwaves—and global warming in general (Ridgwell et al 2009, Zamft and Conrado 2015)—by lowering near-surface air temperatures (Seneviratne et al 2018). Enhanced plant glaucousness due to thicker waxy layers of leaves and/or an increased density of leaf trichomes has been considered as a possible strategy for bioengineering of albedo (Ridgwell et al 2009, Seneviratne et al 2018) even though such a possibility has only been investigated in model experiments based on largely untested assumptions about the actual albedo-changing potential of croplands. Chl deficiency may potentially increase canopy photosynthesis by enabling a better distribution of light within the leaf and the canopy space (Ort et al 2015) as well as increasing the photosynthetic efficiency and productivity through a reduction of lightharvesting antenna size and consequent reduction of the wasteful non-photochemical dissipation of excitation energy (Drewry et al 2014, Long et al 2015, Kirst et al 2018)
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